NEW DELHI — The bomb attacks last month on seven Mumbai commuter trains did more than raise Indian hackles against Pakistan for failing to rein in terrorist groups operating on its soil.

They also underscored a gathering threat for India: a small but increasingly deadly cadre of young and often educated Indian Muslims who are being drawn directly into terrorist operations.

The scale and coordination of the July 11 attacks, a senior Indian government official said, suggest that at least one terrorist cell, made up of fewer than a dozen local people and probably directed and financed by militants based in Pakistan, may have carried out the bombings, which killed 183 people.

In the past, the official said, Indian operatives have aided foreign militants in what he called a benign fashion, sometimes providing little more than shelter or food. "The change is that some of them really know what they are up to," the official said.

Perhaps most important, it touches on India's idea of itself as the world's largest secular democracy, capable of including a multitude of peoples and faiths.

"A small section of the Indian Muslim community has been radicalized," said C.Raja Mohan, a columnist for The Indian Express and a member of the National Security Advisory Board. "That's what makes it that much more challenging for the country as a whole to deal with."

The police have arrested eight men from Mumbai, formerly Bombay, in connection with the attacks, although no details have been disclosed about their possible links to the bombings. Among them are a doctor of traditional Islamic medicine and a largely self- taught software worker.

Six of those arrested are said by the authorities to have trained at terrorist camps in Pakistan run by the militant group Lashkar-e-Taiba.

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Several have been linked to a radical homegrown group, now banned, called the Students Islamic Movement of India.

For all the finger-pointing across the border, the attacks have forced India to confront disquiet among Muslims at home, most of whom have resisted calls to join in Islamic radicalism.

"That is still true to a very, very large extent," said India's national security adviser, M.K. Narayanan. "But what has happened is that a very, very manifest attempt to recruit Indian Muslims is now being done."

Those efforts, he said in an interview on CNN-IBN television, are increasingly directed at educated Indian Muslims and at elements in the military.

Senior Lashkar officials interviewed in Rawalpindi, Pakistani, say no more than 50 Indians attend military and religious training camps in Pakistan and the Pakistani-controlled part of Kashmir on average each year. But they confirmed that an active recruitment drive was under way in India.

It is impossible to say to what extent the still apparently small number of recruits are motivated by essentially Indian grievances - especially the pogroms in 2002 against Muslims in Gujarat, which left 1,100 dead - or by Islamic ideology.

But increasingly, many in India fear, the two are at risk of merging.

Narayanan said that a reminder of anti-Muslim violence in India was a powerful recruitment tool.

"Quite often," he said, "the motivation is, 'You know what happened in Gujarat.'"